The present invention relates to an electrode holder for immersion-type and flow-type measuring systems in analytical chemistry, according to the preamble of claim 1.
It is frequently an indispensable necessity in analytical chemistry that chemical sensors of immersion-type or flow-type measuring systems employed, for example, for the continuous monitoring of biological or chemical processes by corresponding measurements of the analytical parameters of a liquid measuring agent, be calibrated or cleaned. On the other hand, however, these processes are troublesome and time-consuming as in order to permit such operations to be carried out, the respective measuring electrodes, for example, measuring systems for pH, conductivity, oxygen or chlorine measurements, or the like, must be retracted from the measuring agent under process conditions, without there always being the possibility to interrupt the process for this purpose, to drain the measuring agent or to completely block a pipeline for passage by the measuring agent.
It has, therefore, been known (WO 86/07151) to arrange the transducer probe, being part of the measuring system, in a guiding mechanism by which the sensor is held and guided between an operating position and a servicing position, and to provide in addition a stopcock by means of which the area previously occupied by the transducer is shut off relative to the measuring agent when the transducer has been retracted. Consequently, it is the basic principle of such transducer probes that in order to permit any necessary calibration or cleaning operations, or to enable the electrode to be watered for a predetermined period of time, for example, the design of the electrode holder, which reaches into the pipeline containing the measuring agent or into the reaction tank, is selected in such a way that the electrode can be moved from an immersed position into a retracted or withdrawn position, in which case the previously existing connection to the measuring agent is shut off hermetically in a suitable way. It has been known in this connection (DE-PS 2 557 542) to incorporate the electrode in ball valves performing the function of the stopcock, which valves then separate the electrode from the measuring agent when the latter is retracted, thus making it accessible for the cleaning or calibration agents or for other treatments.
It has also been known in this connection (European Patent Application 0271764) to provide around the active electrode area a calibration space, especially for pH electrodes, which is open in the operating position and closed in the servicing position. This is achieved by means of a sleeve mounted for longitudinal displacement in a sliding guide of the electrode holder and accommodating the electrode carrier in its interior, there being further provided first control means by which longitudinal channels are opened and connected to valve connections in the control head of the fittings, which open into the calibration space, so that the latter can be supplied with the respective agent, such as water/cleaning agent, buffer solution, or the like, in the servicing position, while in the operating position all annular spaces, sealing areas and openings of the valve are under the effect of compressed air acting from the inside to the outside.
If the electrode holders use stopcocks, the stopcock bodies of the valve may consist of cylindrical, spherical or conical plugs, which then lead to the advantages and drawbacks typical for these different types.
If ball or cylinder valves are used in such shut-off devices, it is in any case a particularly serious disadvantage that the respective measuring electrode or probe first has to be fully withdrawn from the rotary area of the plug before the connection to the measuring agent, which may contain very disturbing and contaminating substances, can be interrupted by rotating a cylinder-shaped or ball-shaped stopcock element (plug). This leads, however, to contaminated dead spaces in the area of the stopcock element, a fact which may cause considerable trouble, in particular if the agents contain abrasive substances or tend to deposit. Further, it is a problematic aspect that the measuring electrode, and especially its sensitive forward conical portion has to be fully withdrawn, i.e. removed, from the rotary area of the plug before the plug can be rotated, as otherwise the plug, which separates the measuring electrode from the agent, may shear off the sensitive electrode tip, for example, and destroy the measuring system in its entirety. In view of this aspect, it has been known to arrange a suitable impact protection in the forward area of the measuring probe, for example in the form of impact-protection bolts or impactprotection cages, so as to prevent the electrode from being sheared off by the stopcock. However, such protections tend again to collect dirt and lint and this to a degree which may finally lead to complete blocking of the system.
Another disadvantage resides in the fact that a considerable displacement is required to remove the electrode, which together with its sliding holder passes through the plug opening, fully from both the measuring agent and the area of rotation of the plug. This rather long displacement either consumes free working space in the area of the measuring agent, or requires the provision of additional space through expensive constructional measures as the measuring probe must be retracted to the rear the full length by which it dips into the measuring agent.
Ball valves, in particular, provide additional problems being mounted in more or less floating relationship and being symmetrized by suitable packings in the housing of the stopcock, so that ball valves are less suited in connection with those modifications for which the following invention can be used with particular advantage.
Now, it is the object of the present invention to design the area of the stopcock of an electrode holder in such a way that no disadvantageous dead spaces tending to be contaminated or to give other trouble are produced during transfer of the plug from one position to the other.